Topotecan: a new topoisomerase I inhibiting antineoplastic agent

Efficacy of topotecan treatment on antioxidant enzymes and TBA-RS levels in submandibular glands of rabbits: An experimental study

OBJECTIVE:

The aim of this study was to investigate the effects of topotecan (Hycamtin), a topoisomerase I inhibiting anticancer agent, on antioxidant enzymes (SOD, CAT, and GSH-Px) and TBA-RS values of the submandibular glands of the rabbits.

STUDY DESIGN AND SETTING:

The study was conveyed in two groups (Group I, II) and control with a total of 24 rabbits. Eight rabbits in group I received intravenous (i.v.) topotecan (0.25 mg/kg once daily) for 3 days. Eight rabbits in group II received i.v. topotecan (0.5 mg/kg once daily) for 3 days. On the 15th day after administration of topotecan, sub-mandibular glands were removed and levels of the SOD, CAT, and GSH-Px and the TBA-RS in the sub-mandibular glands of the rabbits were examined.

RESULTS:

SOD, CAT, and GSH-Px values were significantly higher in high-dose topotecan group compared to control group ( P < 0.05). SOD and TBA-RS values were significantly higher in high-dose topotecan group compared to low-dose topotecan group ( P < 0.05).

CONCLUSION:

It was concluded that, to prevent the hazardous effects of oxygen free radicals due to topotecan, antioxidant enzymes SOD, CAT, and GSH-Px were increased. The higher levels of the TBA-RS values in group II showed that permanent damage was present because of high-dose topotecan administration in the submandibular glands of the rabbits.

Toward precision medicine in glioblastoma: the promise and the challenges

Integrated sequencing strategies have provided a broader understanding of the genomic landscape and molecular classifications of multiple cancer types and have identified various therapeutic opportunities across cancer subsets. Despite pivotal advances in the characterization of genomic alterations in glioblastoma, targeted agents have shown minimal efficacy in clinical trials to date, and patient survival remains poor. In this review, we highlight potential reasons why targeting single alterations has yielded limited clinical efficacy in glioblastoma, focusing on issues of tumor heterogeneity and pharmacokinetic failure. We outline strategies to address these challenges in applying precision medicine to glioblastoma and the rationale for applying targeted combination therapy approaches that match genomic alterations with compounds accessible to the central nervous system.

Optimal management of Ewing sarcoma family of tumors: recent developments in systemic therapy

The Ewing sarcoma family of tumors (ESFT) is defined by cell surface expression of CD99 and a translocation involving EWS and an ETS partner. Cytotoxic chemotherapy remains the benchmark of first- and second-line therapy, and although the majority of patients with localized disease are cured, almost one third of patients relapse or progress from their disease. Moreover, cure remains elusive in most patients who present with distant metastases. In recent years, the ESFT literature has been dominated by reports of attempts at modulating the insulin-like growth factor (IGF) receptor (IGFR). Unfortunately, three phase II studies examining inhibiting antibodies to IGFR-1 published disappointing results. Whether these results were due to failure to modulate the pathway or other limitations in study design and/or patient selection remain unclear. Other novel strategies currently being investigated in ESFT include tyrosine kinase, mammalian target of rapamycin (mTOR), and poly(ADP-ribose) polymerase (PARP) inhibitors.

The effects of topotecan on lipid peroxidation and antioxidant enzyme levels in rabbit liver tissue

BACKGROUND

To evaluate the possible influence of topotecan therapy on lipid peroxidation and antioxidant enzymes in rabbit liver tissue, the levels of thiobarbituric acid reactive substances (TBARS) and activities of the antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) were investigated.

METHODS

A total of 24 adult, healthy New Zealand rabbits were divided into three groups (n = 8). Topotecan was administered intravenously via the ear vein for 3 days at 0.25 mg/kg/day for the low-dose group and 0.50 mg/kg/day for the high-dose group; physiological saline was used for the control group. All animals were sacrificed on day 15. Livers were removed and homogenised. The homogenate supernatant was used for measurement of TBARS levels, and SOD, GSH-Px, and CAT enzyme activities (expressed as IU/mg protein).

RESULTS

There were significant differences in the TBARS level and GSH-Px activity between control and the topotecan treatment groups. TBARS level of topotecan treatment groups was higher than control (89% and 126%, respectively, P = 0.001). It was also significantly higher in the high-dose group than the low-dose group (20%; P = 0.011). GSH-Px activity was lower in the low- and high-dose topotecan groups than the control (42% [P = 0.002] and 65% [P = 0.001], respectively). Enzyme activity was lowest in the high-dose group and the difference was also significant when compared with the topotecan groups (40%; P = 0.001). Although there was some decrease in SOD and CAT activities in the topotecan-treated groups, differences from the control group were not significant.

CONCLUSIONS

These findings suggest that topotecan treatment results in an increase in lipid peroxidation and a decrease in antioxidant enzyme activities in healthy liver tissue from rabbits. We believe that the addition of antioxidants to topotecan therapy may reduce the harmful effects of topotecan on liver tissue.

Treatment of rat brain tumors using sustained-release of camptothecin from poly(lactic-co-glycolic acid) microspheres in a thermoreversible hydrogel

A thermoreversible gelation polymer consisting of an aqueous solution in the sol state at room temperature and in the gel state near body temperature was examined for its use in the retention of microspheres and sustained, long-term delivery of anti-cancer drugs using a rat model of malignant glioma. The poly(lactic-co-glycolic acid) (PLGA) microspheres containing camptothecin at ratios of 1 : 33 or 1 : 50 mediated sustained release, with approximate 80% of camptothecin released after 28 d. Rats were inoculated in the brain with C6 glioma cells, followed 7 d later by injection in the tumor site with 1 : 33 and 1 : 50 PLGA microspheres dispersed in a thermoreversible gelation polymer (TGP) solution. Kaplan-Meier analysis showed that the mean survival period of the untreated group was 16 d, with a slight increase in rats treated with TGP-only solution, empty or 1 : 50 microspheres in phosphate-buffered saline. The mean survival period of rats treated with the camptothecin powder in TGP was 21 d, while that of rats treated with 1 : 33 and 1 : 50 microspheres in TGP was significantly longer than the untreated group; long-term survival rats were observed. These results suggest that the anti-tumor effect of camptothecin can be enhanced by long-term sustained release from microspheres retained in the rat brain by TGP gel.

A phase II clinical trial of topotecan in Japanese patients with relapsed ovarian carcinoma

OBJECTIVE

This Phase II study was carried out to investigate the efficacy, safety and pharmacokinetics of topotecan in Japanese patients with relapsed ovarian carcinoma.

METHODS

Patients with relapsed ovarian carcinoma after having received one regimen containing platinum-based chemotherapy were eligible for this study. Topotecan was administered at 1.2 mg/m(2)/day for five consecutive days, repeated every 3 weeks.

RESULTS

Seventy-two patients were enrolled in the study. The response rate was 28.2% (95% confidence interval, 18.1-40.1%). Signs of myelosuppression, such as neutropenia (Grade 3, 12.5%; Grade 4, 83.3%), thrombocytopenia (Grade 3, 36.2%; Grade 4, 4.2%) and decreased hemoglobin (Grade 3, 36.1%; Grade 4, 11.1%), were the most common hematological toxicities. Grade 3 febrile neutropenia occurred in 5 (6.9%) patients. There was little intraindividual or interindividual variability in the pharmacokinetics of topotecan.

CONCLUSIONS

Topotecan at 1.2 mg/m(2)/day is an effective and tolerable therapeutic option for Japanese patients with relapsed ovarian carcinoma.

High antimetastatic efficacy of MEN4901/T-0128, a novel camptothecin carboxymethyldextran conjugate

The antimetastatic activity of a novel camptothecan conjugate, MEN4901/T-0128, in which 7-ethyl-10-aminopropyloxy-camptothecin (T-2513) is bound to a biodegradable carboxymethyldextran via a Gly-Gly-Gly linker, was observed in this study. High antimetastatic activity of MEN4901/T-0128 was demonstrated in a clinically-relevant orthotopic mouse model of human colon cancer. MEN4901/T-0128 and irinotecan were compared for anti-metastatic activity as well as efficacy against the primary tumor. An imageable, metastatic model was made by surgical orthotopic implantation (SOI) of the green fluorescent protein (GFP)-expressing HT-29 tumor in nude mice. MEN4901/T-0128 and irinotecan were administered intravenously at various doses and schedules. MEN4901/T-0128, with treatment beginning on d 49 after SOI, was highly effective on lymph node metastasis as well as against the primary tumor. Both GFP imaging and histology demonstrated a markedly lower metastatic incidence of lymph nodes in all MEN4901/T-0128 treated mice compared with irinotecan-treated and untreated mice. At the most efficacious dose of MEN4901/T-0128, only 1 of 12 animals had lymph node metastasis compared with 19 of 20 in the control group. The present study demonstrates the principle that when a camptothecan is conjugated to an appropriate polymer, the drug can become extremely effective with important clinical potential for antimetastatic therapy, a most urgent need.

Topotecan treatment and its toxic effects on hematologic parameters and trace elements

The aim of this study was to investigate the effects of topotecan, a topoisomerase I-inhibiting anticancer agent, on hematologic parameters and serum levels of trace elements. The study was conducted on three groups consisting of 16 and 18 rabbits in the study groups and 15 rabbits in the control group. Rabbits in group I (n = 16) received high-dose topotecan intravenously (i.v.; 0.5 mg/kg once daily), while rabbits in group II (n = 18) received low-dose topotecan i.v. (0.25 mg/kg once daily) for 3 days. The 15 rabbits comprising the control group did not receive topotecan. Serum samples were collected from each rabbit on the first day, before the treatment, and on the 15th day of treatment. Erythrocytes, hemoglobin, white blood cell count, thrombocyte count, and trace elements such as selenium, copper, lead, zinc, and cobalt were analyzed. Hemoglobin levels and erythrocyte counts were lower in both study groups than in the control group. However, thrombocyte and leukocyte counts were similar in all three groups (p > 0.005). Serum trace element levels (copper, lead, zinc, and cobalt) did not differ significantly between groups. However, serum selenium levels were significantly lower in both study groups than the control group (p < 0.001). The results revealed that topotecan treatment causes a decrease in erythrocyte counts and hemoglobin levels due to bone marrow suppression, and these effects must be taken into account during treatment. In addition, selenium supplementation might be helpful in cancer patients receiving topotecan to increase the effect of the chemotherapeutic agent.

Effects of topotecan treatment on nasal, buccal, and lingual mucosa in the rabbit: light and transmission electron microscopic evaluation

Anticancer agents may cause side effects and some of which may be dose dependant. It is important for clinicians to see the effects on tissues histopathologically. The aim of this study was to investigate the effects of topotecan (hycamtin), a topoisomerase I inhibiting anticancer agent, on nasal, buccal, and lingual mucosa of rabbits. The study was carried out in two groups each consisting of 20 rabbits. Rabbits in group I received i.v. topotecan (0.5 mg/kg once daily) for 3 days. Rabbits in group II received i.v. topotecan (0.25 mg/kg once daily) for 3 days. In group I and II, biopsies from the nasal, buccal, and lingual mucosa were taken on the fourth (1 day after the 3-day topotecan treatment) and 15th day (12 days after the 3-day topotecan treatment). Light and transmission electron microscopic (TEM) observations have shown that nasal mucosa was not affected by topotecan administration. Topotecan treatment resulted in the formation of some ulcerative lesions in the lingual mucosa especially on the lower surface of the tongue. On the dorsal surface, the epithelium showed highly edematous and degenerating cells and separations in the stratum granulosum. In the buccal mucosa, effects were similar. In lingual and buccal mucosa, healing was observed on the 15th day. The oral (lingual and buccal) mucosal side effects of topotecan were observed as reversible and not dose dependent. It was concluded that these side effects are not severe, and topotecan may be used safely in cancer treatment.

Effect of pH and human serum albumin on the cytotoxicity of a glucuronide prodrug of 9-aminocamptothecin

PURPOSE

9-aminocamptothecin glucuronide (9ACG) is a prodrug of 9-aminocamptothecin (9AC) that displays potent antitumor activity against human tumor xenografts in nude mice. Camptothecins exist in a pH dependent equilibrium between active lactone and inactive carboxy forms that can be altered by binding to human serum albumin (HSA). Here we investigated the influence of pH and HSA on the lactone-carboxy equilibrium, HSA binding, and cytotoxicity of 9ACG.

METHODS

Microfiltration and HPLC were used to measure the influence of pH on lactone to carboxy conversion and HSA binding of 9ACG as compared to other camptothecins. In vitro cytotoxicity of drugs was determined against EJ human bladder carcinoma cells and CL1-5 human lung cancer cells.

RESULTS

The rate of lactone to carboxy conversion was similar for 9ACG and 9AC. Decreasing the pH from 7.6 to 6.0 increased the equilibrium levels of the lactone forms of the drugs from 20 to almost 95% of total drug. HSA moderately diminished the amount of free 9ACG lactone but did not change the ratio of 9ACG lactone to 9ACG carboxy. Consistent with the effect of pH on lactone levels, lowering the pH of EJ human bladder carcinoma cells from 7.6 to 6.8 decreased the IC(50) of 9ACG from 480 to 98 nM and 9AC from 33 to 12 nM. Activation of 9ACG by human beta-glucuronidase anchored on the surface of EJ cells further decreased its IC(50) value to 26 nM. Although HSA significantly decreased the cytotoxicity of 9AC and 9ACG, activation of 9ACG at cancer cells with an antibody-beta-glucuronidase immunoconjugate produced greater cytotoxicity than 9AC.

CONCLUSIONS

Acidification and targeted delivery of beta-glucuronidase can enhance 9ACG cytotoxicity even in the presence of HSA.

Oncological implications of hypoxia inducible factor-1alpha (HIF-1alpha) expression

Solid tumours contain regions of hypoxia, which may be a prognostic indicator and determinant of malignant progression, metastatic development and chemoradio-resistance. The degree of intra-tumoural hypoxia has been shown to be positively correlated with the expression of the transcription factor hypoxia-inducible factor 1. HIF-1 is composed of 2 sub-units, namely HIF-1alpha and HIF-1beta. The production of hypoxia inducible factor 1-alpha has been identified as a key element in allowing cells to adapt and survive in a hostile hypoxic environment via a variety of pathways. HIF-1alpha is stabilised by hypoxia at the protein level, and also by the oncogenes HER2neu, v-src and ras. There are over 60 target genes for HIF-1, many of which are activated in cancers in comparison to equivalent normal tissues. Chemotherapeutic modulation of HIF-1 pathways has shown promise for patients with chemo-radio resistant or recurrent tumours in Phase II clinical trials. We herein review the existing literature on hypoxia inducible factor-1alpha, particularly its role in carcinogenesis and clinical implications of its over-expression.

Chemotherapy in brain metastases

The use OF chemotherapy to treat patients with brain metastases has been viewed historically with skepticism. To date, a survival benefit has not been demonstrated with the use of systemic chemotherapy in patients with brain metastases. However, the introduction of novel agents and delivery techniques warrants a reexamination of the role of systemic chemotherapy in the management of brain metastases. Temozolomide has shown encouraging results in patients with nonsmall cell lung cancer, and implanted carmustine wafers have demonstrated excellent local tumor control rates. This review discusses clinical data from the past decade with emphasis on trial design, tumor histology, available agents, and multimodality strategies. In addition, delivery techniques that circumvent the blood-brain barrier are reviewed. Although chemotherapy is usually used as a salvage therapy, it may be considered for use in selected patients with newly diagnosed brain metastases. To better evaluate chemotherapy in brain metastases, future trials should evaluate novel agents in the preirradiation setting. Enhanced regional delivery methods warrant further investigation, and Phase III trials of current regimens stratified by histology and by prognostic factors will establish the role of specific chemotherapy regimens in the treatment of patients with brain metastases.

A predictive model of human myelotoxicity using five camptothecin derivatives and the in vitro colony-forming unit granulocyte/macrophage assay

PURPOSE

Many promising anticancer drugs are limited by myelosuppression. It is difficult to evaluate human myelotoxicity before a Phase I study because of the susceptibility of humans and animals to hematotoxicity. The purpose of this study was to establish a reliable method to predict the human maximum tolerated dose (MTD) of five camptothecin derivatives: SN-38, DX-8951f, topotecan, 9-aminocamptothecin, and camptothecin.

EXPERIMENTAL DESIGN

The myelotoxicity of SN-38 and DX-8951f were evaluated on bone marrow from mice, dogs, and humans using a 14-day colony-forming unit, granulocyte-macrophage (CFU-GM) assay to determine the 50%, 75%, and 90% inhibitory concentration values (IC50, IC75, and IC90, respectively).

RESULTS

Species differences in myelotoxicity were observed for SN-38 and DX-8951f. Using human and murine IC90s for myelotoxicity of these compounds and other camptothecin compounds (topotecan, 9-aminocamptothecin, and camptothecin), in vivo toxicological data, and pharmacokinetic parameters (data referred to in the literature), human MTDs were predicted retrospectively. The mechanism-based prediction model that is proposed uses the in vitro camptothecin assay and in vivo parameters on the basis of free fraction of area under the concentration-curve at the MTD (r2 = 0.887) and suggests that the human MTDs were well predicted for the five camptothecin derivatives by this model rather than by other models.

CONCLUSION

The human MTDs of the camptothecin drugs were successfully predicted using the mechanism-based prediction model. The application of this model for in vitro hematotoxicology could play an important role for the development of new anticancer agents.

Interactions Between Antiretrovirals and Antineoplastic Drug Therapy

Despite the established impact of highly active antiretroviral therapy (HAART) in reducing HIV-related morbidity and mortality, malignancy remains an important cause of death. Patients who receive the combination of cancer chemotherapy and HAART may achieve better response rates and higher rates of survival than patients who receive antineoplastic therapy alone. However, the likelihood of drug interactions with combined therapy is high, since protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) are substrates and potent inhibitors or inducers of the cytochrome P450 (CYP) system. Since many antineoplastic drugs are also metabolised by the CYP system, coadministration with HAART could result in either drug accumulation and possible toxicity, or decreased efficacy of one or both classes of drugs. Although formal, prospective pharmacokinetic interaction studies are not available in most instances, it is possible to infer the nature of drug interactions based on the metabolic fates of these agents. Paclitaxel and docetaxel are both metabolised by the CYP system, although differences exist in the nature of the isoenzymes involved. Case reports describing adverse consequences of concomitant taxane-antiretroviral therapy exist. Although other confounding factors may have been present, these cases serve as reminders of the vigilant monitoring necessary when taxanes and HAART are coadministered. Similarly, vinca alkaloids are substrates of CYP3A4 and are, thus, vulnerable to PI- or NNRTI-mediated changes in their pharmacokinetics. Interactions with the alkylating agents cyclophosphamide and ifosfamide are complicated as a result of the involvement of the CYP3A4 and CYP2B6 isoenzymes in both the metabolic activation of these drugs and the generation of potentially neurotoxic metabolites. Existing data regarding the metabolic fate of the anthracyclines doxorubicin and daunorubicin suggest that clinically detrimental interactions would not be expected with coadministered HAART. Commonly used endocrine therapies are largely substrates of the CYP system and may, therefore, be amenable to modulation by concomitant HAART. In addition, tamoxifen itself has been associated with reduced concentrations of both anastrozole and letrozole, raising the concern that similar inducing properties may adversely affect the outcome of PI- or NNRTI-based therapy. Similarly, dexamethasone is both a substrate and concentration-dependent inducer of CYP3A4; enhanced corticosteroid pharmacodynamics may result with CYP3A4 inhibitors, while the efficacy of concomitant HAART may be compromised with prolonged dexamethasone coadministration. Since PIs and NNRTIs may also induce or inhibit the expression of P-glycoprotein, the potential for additional interactions to arise via modulation of this transporter also exists. Further research delineating the combined safety and pharmacokinetics of antiretrovirals and antineoplastic therapy is necessary.

Stability of the new prodrug 9-aminocamptothecin glucuronide (9ACG) in the presence of human serum albumin

9-aminocamptothecin glucuronide (9ACG) is a new water-soluble prodrug of 9-aminocamptothecin (9AC) that is a substrate for beta-glucuronidase and displays potent antitumor activity against human tumor xenografts. The lactone ring of camptothecins (CPTs) is required for antitumor activity but spontaneously opens under physiological conditions to an inactive carboxy form. The carboxy form of many CPTs, including 9AC, preferentially binds to human serum albumin (HSA), which further reduces the equilibrium amount of active lactone and greatly decreases antitumor efficacy. In this study, we examined the hypothesis that the unique structure of 9ACG might alter prodrug interaction with HSA and increase 9ACG lactone stability as compared with 9AC. HPLC analysis revealed that HSA did not affect the equilibrium level of 9ACG lactone whereas both CPT lactone and 9AC lactone were greatly reduced in the presence of HSA as compared to their equilibrium levels in PBS. Similar results were found in human serum and whole blood. The lactone ring of 9ACG also opened more slowly (t(1/2)=50 min) as compared with 9AC (t(1/2)=20 min) in the presence of HSA. Both 9ACG lactone and 9ACG carboxy bound HSA with similar affinities (K(D) approximately 4.5 x 10(-5)M(-1)). Binding of 9ACG to HSA reduced prodrug toxicity to cancer cells by about 10-fold in vitro. Injection of HSA into nude mice prolonged the half-life of 9ACG by about 3-fold, indicating that albumin-bound 9ACG lactone may act as a depot of active prodrug in vivo. Our results suggests that in contrast to CPT and 9AC, HSA does not appear to adversely affect 9ACG and may enhance the selective antitumor activity of 9ACG in tumors that contain beta-glucuronidase.

Efficacy of topotecan treatment on an experimental model of transient evoked otoacoustic emissions

OBJECTIVE

The aim of this study was to investigate the effects of topotecan (Hycamtin), a topoisomerase I inhibiting anticancer agent, on Transient Evoked Otoacoustic Emissions (TEOAEs) of the rabbits. We planned to investigate whether this test might provide a method for monitoring early ototoxic influence of drug administration to the cochlea.

METHODS

The study was conveyed in two groups each consisting of five rabbits with a total of ten ears. Rabbits in group I received i.v. topotecan (0.5 mg/kg once daily) for 3 days. Rabbits in group II received i.v. topotecan (0.25 mg/kg once daily) for 3 days. Cochlear function was serially monitored using transient evoked otoacoustic emissions before administration (BA) and on the 4th and 15th days after administration of topotecan. TEOAEs were analysed in terms of mean stimulus, stability and emission amplitude at 1.0-4.0 kHz.

RESULTS

For group I and II, intergroup and intragroup differences were not statistically significant in the mean stimulus, stability and emission amplitudes at 1.0-4.0 kHz.

CONCLUSIONS

We evaluated the potential role of TEOAEs in early identification of cochlear dysfunction induced by topotecan. It was concluded that topotecan did not have ototoxic effects on the cochlea in the early period of administration. TEOAEs may be useful to monitor the cochlear function and to detect the late stage of ototoxicity especially in the presence of potentially toxic factors for the prevention of permanent damage.

Topotecan for Ovarian Cancer and Small-Cell Lung Cancer

The increasing complexity of cancer chemotherapy makes it mandatory that pharmacists be familiar with these highly toxic agents. This column reviews various issues related to the preparation, dispensing, and administration of cancer chemotherapy, both commercially available and investigational.